So the fluid solver crashes with an floating point exception and with that the solid solver ends communication without an error.

The fluid solver output:

```
Courant Number mean: 1.24619 max: 12.2085
Time = 0.68
smoothSolver: Solving for cellDisplacementy, Initial residual = 0.0181902, Final residual = 9.9823e-07, No Iterations 182
[0]PETSC ERROR: ------------------------------------------------------------------------
[0]PETSC ERROR: Caught signal number 8 FPE: Floating Point Exception,probably divide by zero
[0]PETSC ERROR: Try option -start_in_debugger or -on_error_attach_debugger
[0]PETSC ERROR: or see https://www.mcs.anl.gov/petsc/documentation/faq.html#valgrind
[0]PETSC ERROR: or try http://valgrind.org on GNU/linux and Apple Mac OS X to find memory corruption errors
[0]PETSC ERROR: configure using --with-debugging=yes, recompile, link, and run
[0]PETSC ERROR: to get more information on the crash.
[0]PETSC ERROR: User provided function() line 0 in unknown file
--------------------------------------------------------------------------
MPI_ABORT was invoked on rank 0 in communicator MPI_COMM_WORLD
with errorcode 59.
NOTE: invoking MPI_ABORT causes Open MPI to kill all MPI processes.
You may or may not see output from other processes, depending on
exactly when Open MPI kills them.
--------------------------------------------------------------------------
```

The output from an iteration before:

```
Courant Number mean: 1.43696 max: 5.28101
Time = 0.67
smoothSolver: Solving for cellDisplacementx, Initial residual = 0.019039, Final residual = 9.99036e-07, No Iterations 203
smoothSolver: Solving for cellDisplacementy, Initial residual = 0.0149607, Final residual = 9.98013e-07, No Iterations 137
DICPCG: Solving for pcorr, Initial residual = 1, Final residual = 9.56222e-09, No Iterations 102
DICPCG: Solving for pcorr, Initial residual = 0.000108822, Final residual = 7.19479e-09, No Iterations 79
time step continuity errors : sum local = 5.22968e-13, global = 1.52252e-14, cumulative = 1.246e-08
smoothSolver: Solving for Uy, Initial residual = 0.00662969, Final residual = 1.52762e-07, No Iterations 4
DICPCG: Solving for p, Initial residual = 0.579885, Final residual = 0.000408769, No Iterations 73
DICPCG: Solving for p, Initial residual = 6.08125e-05, Final residual = 4.35898e-08, No Iterations 67
time step continuity errors : sum local = 7.24805e-08, global = -3.5555e-10, cumulative = 1.21044e-08
DICPCG: Solving for p, Initial residual = 0.0166688, Final residual = 1.2164e-05, No Iterations 69
DICPCG: Solving for p, Initial residual = 2.15173e-05, Final residual = 1.95785e-08, No Iterations 45
time step continuity errors : sum local = 5.17453e-08, global = -1.18473e-08, cumulative = 2.57179e-10
DICPCG: Solving for p, Initial residual = 0.00910024, Final residual = 8.23503e-06, No Iterations 69
DICPCG: Solving for p, Initial residual = 1.34088e-05, Final residual = 1.11752e-08, No Iterations 65
time step continuity errors : sum local = 3.63172e-08, global = -1.63888e-09, cumulative = -1.3817e-09
DICPCG: Solving for p, Initial residual = 0.00615916, Final residual = 5.598e-06, No Iterations 69
DICPCG: Solving for p, Initial residual = 8.67066e-06, Final residual = 9.91412e-09, No Iterations 60
time step continuity errors : sum local = 3.60104e-08, global = -2.50135e-09, cumulative = -3.88305e-09
ExecutionTime = 127.99 s ClockTime = 174 s
```

I guess the courant number before the crash is quite high compared to the mean value and the one from an iteration before.

In the beginning it also solves for Ux with the smooth solver, but that entry is also missing at some point.